Ceramic materials are hard, brittle, heat-resistant and corrosion-resistant substrates made by shaping and then heating a non-metallic mineral, such as clay, at a high temperature. Enamels, porcelain, bricks, and glasses are examples of materials that are produced by molding or shaping minerals and baking or firing them at high temperatures.
Glass is a hard, brittle and often transparent solid that is used, for example, in the construction of windows, bottles and lenses. Many types of glass contain silica as their main component. Common types of glass include, inter-alia, soda-lime glass, borosilicate glass, boron and/or phosphorous doped glass, silicon dioxide, silicon nitride, and aluminum oxynitride.
In general, frosted glasses has the effect of rendering the glass translucent by scattering of light during transmission, thus blurring images view while still transmitting light.
Providing a non-colored pattern to glass or ceramic substrates may be used for example, in architecture, to give rough, opaque or “matt” patterns or may be used, for example, in surfaces on windows or glass doors both for aesthetic purposes and for avoiding accidental collisions.
A frost appearance of glass has traditionally been performed by physical (mechanical) or chemical etching processes.
In the physical process fine particles of sand are blasted against an unprotected portion of the surface to be decorated according to a mask. The sandblasting erodes the unmasked portion of the glass surface to produce a frosted appearance that provides a contrast for the untouched smooth transparent part of the glass. This process is tedious and costly.
Chemical etching comprises dipping or coating a glass or mask-covered glass in or with an etching composition containing strong acids such as hydrofluoric acid, nitric acid, hydrochloric acid, and sulfuric acid, creating a desired etched pattern. However, the strong acids used in conventional chemical etching processes cause a number of serious problems. Namely, during the etching step, poisonous gases, which are harmful to humans, are generated. Also, the waste water produced during such processes needs to be treated in a safe manner so as not to raise environmental pollution, including water pollution, air pollution and the like. Due to these problems, chemical etching has not been widely practiced in well developed nations on an industrial scale and thus, cannot fulfill increasing demands for frosted glass.
Several methods are available for decorating glass and ceramics with high-quality images. The coating and printing processes used for glass and ceramic printing rely on a variety of paste and ink systems. Some of these inks are inorganic.
Ceramic colors, as inorganic ceramic inks are known, are a mixture of mineral-based pigments (metal oxides and salts) and finely ground glass particles, called frit. These materials are fused to the ceramic substrate surface on which they are coated or printed by calcining (“firing”) them at temperatures between 500-1450° C. Firing temperatures vary depending on the make-up of the color, the nature of substrate, and other application criteria. While these inks are typically called “inorganic”, they may also contain small amounts of organic material. The organic components are the materials in which the pigment and frit are suspended to create a printing ink. These organic materials are expected to burn out during firing without affecting print quality and final color.
In some cases, screen printing, pad printing, offset printing, flexographic printing, gravure printing, roller coating, dip coating, curtain coating, air brushing, or other coating, spraying and analog printing techniques are (or can be) used to imitate a frost appearance on glass. These techniques require the preparing of plates, cylinders, masks or screens as a master copy, which must be maintained and stored, and then used to print the image on the glass or the ceramic substrate over and over again. The frost appearance in these coating and printing techniques can be achieved by using frost-imparting ink or pastes containing a combination of glass frits, in which a high melting frit is included, and/or ceramic (or inorganic) particles having an average particle size above several micron. Such ink paste products are also highly viscous, since they contain high concentration of the particles. After firing, a frosted appearance is produced by the high melting frits and/or the ceramic (or inorganic) particles remaining on the surface.